Burton considered this for a moment. “You propose that madness springs from an inability to cope with a mental shock?”

“In cases of monomania, yes. There are, of course, a great many instances where the cause can be traced to a physical imbalance, but with Mr. Oliphant—he was an opium addict, you know?”

“Yes, I’m aware of that.”

“Well then, I suspect he was so petrified by a nightmarish vision induced by the drug that he lost his—ugh!—mind in order to escape it. It is my supposition that the hallucination involved rats, and he is now trying to recreate it. You see, there is method in his madness.”

“To what end, Doctor?”

“If he manages, independently, to reproduce his hallucination, he will achieve mastery over it. Or, to put it another way, if he can knowingly reconstruct what he experienced, he can also knowingly destroy it, thus breaking the shackles of terror that—ugh!—bind him.”

Burton brushed dust from his trouser leg, nodded slowly, and said, “Very well, your theory sounds eminently plausible, but how does this relate to Galton’s escape?”

Monroe’s face spasmed again and his right arm jerked outward. He pulled the errant limb back to his side and held it there with his left hand.

“About fifteen years ago, Galton suffered a severe nervous breakdown and was brought here to recover. He never did. Instead, he developed an idée fixe concerning the transmutability of the flesh.”

“Meaning what?”

“Meaning he believes animals can be artificially raised to a human standard of intelligence, and that humans can, through scientific means, be made into something akin to—ugh!—gods.”

“Again—this concerns Oliphant how?”

“I’m coming to that, Mr. Cribbins. You see, Oliphant’s delusion involves the conviction that a god of some sort is seeking incarnation in the flesh.”

Burton recalled what Monckton Milnes had told him about the magic squares.

Monroe continued, “Since Galton’s misconception concerning artificially constructed gods is—ugh!—thematically similar, I thought it might be enlightening to put the two men together. I hoped they would either cancel out each other’s delusions or hasten each other toward a conclusion to their—ugh!—ugh!—demented fantasies.”

“And what happened?”

“During their fourth encounter, last night, Oliphant flew into a rage and attacked his attendants. While they were distracted, Galton broke into a storage room and climbed out through its window.”

Burton opened his mouth to speak but was stopped by a gesture from Monroe. “No, Mr. Cribbins, the window was not left open by accident. We are—ugh!—meticulous about security here. The fact is—it was forced from the outside.”

Burton leaned forward in his seat. “By whom, Doctor?”

Monroe shrugged. “I don’t know, but a ladder was left behind on this side of the perimeter wall, which means not only that Galton had help to get away, but also that whoever assisted him knew Oliphant would provide a diversion at that—ugh!—particular moment. I can’t for the life of me think how such a thing could be arranged.” He hesitated then added, “Although suspicion must naturally fall on Mr. Darwin.”

“Darwin?”

“Charles Darwin. The Beagle fellow.”

“What has he to do with it?”

“He and Galton are half-cousins. As one of our long-term and most docile patients, Galton was allowed to send and receive letters. Darwin is the only person he has ever corresponded with, and he did so on a regular basis. It’s our policy here to monitor all incoming and outgoing post. The communication between the two men appeared purely—ugh!—scientific in nature. Darwin is apparently on the brink of publishing a theory that might alter the way we think about—ugh!—creation itself. It bears some relation to Galton’s preoccupation, and I was hoping that I might gain a better understanding of my patient’s fixations by reading their missives. Unfortunately, all I could glean from them is that both men are engrossed in disturbingly godless matters which make little—ugh!—sense to me. If any escape plans were discussed between them, then it was done in code and I didn’t detect it.”

“I should like to see those letters.”

“I’m afraid Galton took them with him.”

Pushing his chair back, Burton stood. “Then take me outside. Show me the window.”

“Is that necessary?”

“It is.”

Reluctantly, Monroe got to his feet and led Burton from the office, down the corridor, through the vestibule, and out of the building. They turned left and followed the edge of a long flower bed that skirted the foot of the hospital’s front wall.

“Here.” Monroe pointed to a small window set five feet from the ground.

Burton turned away from it and examined the terrain. He saw six trees huddled together nearby, providing shadows and cover; a long, squarely trimmed hedge beyond them, bordering a large vegetable garden; and more trees between that and the high wall, which they partially concealed.

“A good escape route,” he muttered. “Lots of concealment.”

Returning his attention to the window, he saw gouges in its frame, suggesting the application of a crowbar. He squatted and scrutinised the flower bed.

“Look at these indentations in the soil, Doctor.”

“Footprints, Mr. Cribbins?”

“Yes. Peculiar ones, at that. See how square the toes are, and how small and high the heels?”

“High?”

“Revealed by the indentation. This style has been out of fashion for half a century. It’s the variety of footwear that usually has a large buckle on top. I haven’t seen anyone shod in such a manner since my grandfather.”

“Are you suggesting that Galton’s accomplice was an—ugh!—old man, sir?”

“Two men broke the window, Doctor. And it doesn’t necessarily follow that because their footwear was old, so were they.” Burton straightened. “Two sets of prints. Both men wore the same style of footwear. One had long, narrow feet, the other, short, wide ones. The latter individual was the heavier of the pair.”

Damien Burke and Gregory Hare.

There was no doubt about it. Burton had seen plenty of newspaper illustrations of the notorious duo. Their famously old-fashioned attire, which included buckled shoes, had been the delight of Punch cartoonists. And Hare was shorter but far bulkier than Burke.

So, having failed to kidnap Isambard Kingdom Brunel, they’d got Francis Galton.

Why?

“I think it’s high time I saw Oliphant, Doctor.”

Monroe spasmed, nodded, and accompanied the explorer back the way they’d come. When they reached the lobby, he rang a bell and waited until two attendants appeared. Both were wearing stained leather aprons. Ordering them to follow, he then ushered Burton up a flight of stairs and toward the west wing of the asylum. They passed along cell-lined hallways and were assailed by shouts and screams, incoherent babbling, pleading, and curses. The odour of human sweat and excrement was worse even than the foulest-smelling of the many swamps Burton had struggled through in Africa.

More passageways, more staircases, until on the fourth floor, a door blocked their path. One of the attendants produced a bunch of keys and set about opening it.

“Ugh!” Monroe jerked. “You’ll find fewer patients in this next area, but the ones we keep here are among the most seriously—ugh!—deranged and can be exceedingly violent. They’ll watch our every move through the slots in their cell doors. Please refrain from making eye contact with them.”

The portal’s hinges squealed as the attendant pushed it open. They passed through into yet another filthy corridor. A nurse greeted them.

“This is Sister Camberwick,” the doctor said. “She oversees this section. Sister, this is Inspector Cribbins of the Government Medical Board. He wishes to interview Mr. Oliphant. Is the patient quiet?”

After bobbing to Burton, the nurse replied, “He is, Doctor.”